This invention relates to polycarboxylic acid polymers, which are used as thickeners, emulsifiers and suspending aids, having improved wettability and dispersability. In particular, this invention relates to interpolymers of olefinically unsaturated carboxylic acids or anhydrides and a steric stabilizing component where the interpolymer has admixed therewith a wetting additive, such as a low surface tension surfactant, a glycol, a polyhydric alcohol, or mixtures thereof. The result is a polymer having improved wettability. In addition, we have developed a process for improving the wettability of interpolymers by adding the interpolymer to an aqueuous media containing a low surface tension surface active agent.
Carboxyl containing polymers of vinyl or vinylidene monomers containing at least one terminal CH.sub.2 .dbd.C&lt;group are well known. Such polymers may be homopolymers of unsaturated polymerizable carboxylic acids, such as acrylic acid, methacrylic acid, maleic acid, maleic anhydride, itaconic acid and the like; or copolymers of said acid or anhydride monomers with (meth)acrylate esters, (meth)acrylamides, olefins, maleic anhydrides, vinyl esters, vinyl ethers, and styrenics; or copolymers with other vinyl or vinylidene monomers. Copolymers of these acids may be cross-linked with small amounts of crosslinking agents. These materials are normally prepared by polymerization with a free radical catalyst in an organic medium in a closed vessel or autoclave equipped with stirring. During polymerization, the polymer precipitates from the solution as it is formed. The precipitated polymer is recovered and dried to remove residual solvent. The polymer, now in a powder form, is used by dispersing it in water and neutralizing it to use its thickening, suspending or emulsifying ability. Such polymers are disclosed in U.S. Pat. Nos. 2,798,053; 3,915,921; 3,940,351; 4,062,817; 4,066,583; and 4,267,103.
Polycarboxylic acid polymers in powder form historically have proven difficult to disperse in aqueous media, such as water. Special and often burdensome measures are typically required. Due to their very strong hydrophilic nature, particles of such polymers immediately begin swelling upon contact with water. When a large number of powder particles are added as a group to water, during swelling, a skin of hydrated particles can form around other dry particles before those dry particles can themselves be hydrated. The result is lumps of undispersed particles which cannot be easily eliminated. This phenomena is evident even when a small quantity (one gram or less) of crosslinked polyacrylic acid powder is dropped into water that is being agitated. To overcome these difficulties, special methods are used, such as dusting the powder over agitating water through the use of a sieve, use of a venturi eductor, or employment of a mechanical disperser, but they can slow processing, create high levels of airborne dust, and/or necessitate large capital expenditures.
It has been found, in copending U.S. patent application Ser. No. 07/935,616, filed Aug. 26, 1992, now U.S. Pat. No .5,288,814, that the incorporation of a steric stabilizer into the polymeric network can improve the dispersion of crosslinked polyacrylic acid powders into water. The polymer is less hydrophilic, and so the individual powder particles swell slowly, avoiding the rapid creation of a skin that would otherwise prevent hydration of all powder particles. When steric-stabilized crosslinked polyacrylic acid powder is added to water, one observes the absorption of water into the powder. As the particles wet, they form soft clusters of hydrated particles which eventually sink below the surface of the water. Once the particles are wetted out, they will begin to disperse throughout the water. Upon neutralization with an organic or inorganic base, the hydrated particles and clusters of hydrated particles greatly expand, eventually resulting in a smooth gel or viscous liquid.
Surfactants have been employed in the manufacture of carboxyl containing polymers because, in their manufacture, the aggregation of the polymer can interfere with the polymerization reaction by retarding access of the monomer to free radicals and by interfering with the removal of the heat produced by the polymerization. Further, the precipitated polymer forms a slurry in the solvent which becomes extremely thick, resulting in ineffective mixing and fouling on reactor surfaces. Even the presence of these surfactants does not result in a polymer having improved handling. These surfactants have not been considered low surface tension surfactants. A low surface tension surfactant would be a surfactant that is used as a wetting agent and capable of reducing the surface tension of water, which is about 72 dynes per centimeter at 25.degree. C. to about 40 dynes/cm or less. Surface tension is usually measured using the Denooy Ring or Wilhelmy Plate Method.
For example, U.S. Pat. No. 4,375,533 to Park et al. discloses a process for overcoming some of the above problems, in which the polymerization of acrylic acid, and optional comonomers, in an organic media, is characterized by the use of nonionic surface active agents having a hydrophobe to lipophobe balance (HLB) values between 1 and about 10. U.S. Pat. No. 4,419,502, to Sehm, disclosed a process for the polymerization of acrylic acid and optional comonomers in the presence of a nonionic surface active agent selected from polyoxyethylene alkyl ethers and polyoxyethylene sorbitol esters and having an HLB value greater than 12. U.S. Pat. No. 4,420,596, to Lochhead et al., disclosed a process for polymerizing carboxylic acids in mineral spirits, employing nonionic surface active agents having HLB values less than 10. U.S. Pat. No. 4,526,937 to Hsu teaches the polymerization of acrylic acid in an organic solvent with a free radical catalyst, using nonionic block copolymers of propylene oxide and ethylene oxide to minimize undesirable flocculation and agglomeration. U.S. Pat. No. 4,692,502 to Uebele et at. teaches a process for polymerizing acrylic acid in an organic media with a free radical catalyst and at least one oil-soluble ionic surfactant selected from an anionic formula, a cationic formula, or an amphoteric formula to achieve reduced polymer build-up in the reactor and provide a more desirable particle size for the precipitated polymer.
Low surface tension surfactants have been employed in polymerization processes, involving the polymerization of ethylene and chlorotrifluoroethylene in an aqueous emulsion, such as in U.S. Pat. No. 4,482,685 to H. B. Chin et al, where a water soluble fluorosurfactant, such as Forathc or Fluorad surfactant, is employed. But, this use is in the polymerization per se and not to benefit the polymer after polymerization. Further, U.S. Pat. No. 4,310,698 to T. W. Cooke teaches fluorochemical surfactants for use as wetting agents, rinse aids and leveling agents, while U.S. Pat. No. 4,594,200 to G. S. Penny teaches the use of perfluoro-substituted compounds to reduce the tendency of surfaces to wet in increasing hydrocarbon production from subterranean formations.